If Scotland does reject independence on Thursday, David Cameron, Nick Clegg and Ed Miliband will need to quickly send a giant thank you card to the last person they expected to - Gordon Brown.

The former prime minister is now the de facto leader of the No campaign, pushing Alistair Darling's hesitant, apologetic performances into the shadows.

Watching some of Mr Brown's fiery speeches in the last few days, you can't help but wonder how different his time in Downing Street could have been.

Imagine this combative, angry, fired up version, Brown 2.0, taking on David Cameron in the Commons.

Of course, it would never have happened. The Gordon Brown who finally made it into Number 10 in 2007 was exhausted by ten years of battling Tony Blair, poisoned by the emnity between them, not to mention voter fatigue after a decade of Labour government.

This new Gordon Brown was forged in the failures and frustrations of his short premiership, and bolstered by the freedom of backbench anonymity.

Why is he so fired up? Because he hates Scottish nationalism, loathes the SNP, and seems more determined to defeat Alex Salmond than he ever was during the 2010 election campaign.

It's a particularly bitter turn off events for Mr Darling, one again eclipsed by Brown. But he is the architect of his own marginalization.

Against the Yes campaign's hyperbolic promises and dreams, he's apologetically asked voters to say "no thanks", playing on fears of economic collapse rather than setting out a positive argument for staying in the UK.

There's no doubt it took leaders at Westminster far, far too long to realise the huge danger, their slow sleepwalk to defeat on Thursday. Voters have every reason to be sceptical about grandiose promises of further devolution made so late in the eleventh hour.

But if Scottish voters do reject independence, it will be the much derided former prime minister who deserves much of the credit.